The Secret Life of Rumen Microbes

Paul Weimer, Ruminant MicrobiologistU.S. Dairy Forage Research Center, USDA-ARS

IntroductionThe rumen of the dairy cow is one of the richest and most productive microbial habitats on earth.But what exactly are these microbes? How important are they? What do they do?Can we do anything to make them do their jobs better?

Q U E S T I O N

What’s so important

about rumen microbes?

A N S W E R• Rumen microbes are the foundation of ruminant

animals: Without them the cow would die.

BossyFor lack of

microbes, she was lost

Q U E S T I O N

What do microbes do for the cow?

A N S W E R

• Convert carbohydrates to volatile fatty acids (VFA), the main energy source for cow and main source of fat for milk.

• Convert non-protein N to high-quality microbial protein, used by the cow.

• Metabolize some plant toxins.

The microbes feed the cow! In other words, you are not feeding the cow, you are feeding the microbes. The microbes:

Q U E S T I O N

Does the cow do anything

for the microbes?

A N S W E R• Ingests feeds for microbial

fermentation• Performs rumination to

grind feed particles to small size

• Removes fermentation products to prevent inhibition of microbial growth

A N S W E R• Maintains a favorable environment for

rumen microbes• Anaerobic (no oxygen)• Temperature near microbial optimum of 102 oF• pH around 5.5 to 6.8

Perfect environment!

How were rumen

microbes first discovered?

Q U E S T I O N

A N S W E R

• Gmelin (1831) noted that plant fiber was converted in the rumen to acetic and butyric acids.

• Gruby and Delafond (1843) – first to observe rumen microbes (protozoa).

• Zuntz (1879) – determined that VFA and gas production in the rumen were due to microbial fermentation.

1831

1843

1879

A N S W E R

• Hungate (1948) –developed methods for cultivating rumen microbes in the laboratory.

1948

How much did we know about them back then?

Q U E S T I O N

A N S W E R

• Digesta contents removed from the cow actively fermented plant material in culture vessels.

• Understanding microbial activities required the laborious isolation of pure cultures under anaerobic conditions.

A N S W E R• Only about 2 dozen species

were isolated and their metabolic activities characterized.

• Rumen microbes participate in all of the important nutrient transformations in the rumen (carbohydrate and protein fermentation, methane and CO2 production, protein synthesis).

Q U E S T I O N

What kind of rumen

microbes are there, and what

do they do?

A N S W E R

MICROBIALGROUP

% of Cell

Number

% of Microbial

WeightWhat they do

Bacteria ~ 98% ~ 60%Ferment fiber, starch, sugars, protein, and more

Archaea 1% < 1% Produce methane gas

Protozoa 1% ~40% Eat bacteria, ferment starch

Fungi < 1% 1-3 % Help break down fiber

Are there “good” and

“bad” rumen microbes?

Q U E S T I O N

A N S W E R

IMPORTANT POINT: Because the microbes function as an interactive community, some seemingly “bad bugs” are still necessary for proper rumen function!

“Good bugs”• Fiber digesters• Most other carbohydrate

fermenters• Lactic acid degraders• Detoxifiers

“Bad bugs”• Methane producers• Hyper ammonia-producers• t10,c12-CLA producers• Protozoa

Well, sort of…..

What changed our ability to learn more about the

microbes?

Q U E S T I O N

A N S W E R

The techniques of molecular biology

Whole-genome sequencing Metabolic capabilities of individual species

Species composition and abundance

Microbiologists now have the ability to track specific populations within the rumen and determine how these are impacted by feeding and management, and how they relate to animal performance.

Community fingerprinting methods Quantitative PCRMetagenomic sequencing

So what more have we learned recently?

Q U E S T I O N

A N S W E R• Only ~10% of the species in

the rumen have been identified and cultured in the lab.

• Each cow contains a small set of microbial species (the “core microbiome”) present in nearly every cow.

But,The overall microbial community is unique to each individual cow. A cow and her rumen microbes are well-matched partners.

How stable is the microbial community in

the rumen?

Q U E S T I O N

A N S W E R• The community is very dynamic, with changes

within and across daily feeding cycles, but• Overall, the community is relatively specific for

each cow.

• The community displays “functional redundancy”.

• The community is surprisingly resilient when changes are introduced.

What type of research is

taking place right now?

Q U E S T I O N

A N S W E R• Linking specific members of the rumen

community to nutritional outcomes• Feed efficiency• Milk fat production• Rumen acidosis

• Search for new ways to control undesirable microbial activity

• Methane productionEvaluating the role of the rumen community

in affecting health, immune response, etc.

What can you do to help a

cow’s microbes work better?

Q U E S T I O N

A N S W E R

• Avoid sudden changes in rumen conditions.• Introduce new feed sources and rations gradually

over the course of several feedings.• Avoid pushing rumen temperatures outside the

comfort zone of the microbes• Cold water, frozen silage• Heat stress

• Recognize that the microbial communities of individual cows will respond differently to the same feeding and management.

What do we still need to

learn?

Q U E S T I O N

I have given years of study to the dairy cow and I believe I know a good deal about her, but more and more I am convinced that the darkest place in the world is the inside of a dairy cow. Chemists have their laboratory, mechanics may have their machines, but no man knows how the dairy cow transforms the hay and grain she eats into milk.

W.D. Hoard, EditorHoard’s Dairyman, ca. 1885

We know much more today about the rumen than we did in 1885, but we still have much to learn.

A N S W E R

• What exactly are those other 90% of the community doing?

• Can we dictate rumen community composition by how we feed and raise the calf or heifer?

• How can we get probiotic strains to persist in the rumen?

• Can rapid testing of the rumen community composition guide us to feeding cows more intelligently?